Line selector switch



April 18, 1944. Q DEAKlN 2,346,911

LINE SELECTOR SWITCH Filed Feb. 5, 3.942 2 Sheeis-She l5.

lNvENTQR GERALD Dil/#K IN ATTRNEY 2 Sheets-Sheet 2 FIG.3.

G. DEAKIN LINE SELECTOR SWITCH Filed Feb. 5, 1942 MALLA AAAAA April 18, 1944.

Patented Apr. 18, 1944 LINE SELECTOR SWITCH Gerald Deakin, International- New York, N. Y.. assigner to. Standard Electric Corporation,

New York, N. Y., a corporation of Delaware Application February 5, 1942, Serial No. 429,654

8Claims.

` mechanical switching device particularly suitable for use as a line nder, link finder, or trunk finder in such systems.

In accordance with the present invention the line, link or trunk whichis marked by application of a distinctive potential to a conductor associated therewith, is found or identified by means, device, such as a vacuumA of a very sensitive test tube test device, which requires extremely small currents for its response, and the apparatus for associating such highly sensitive test device with the marked conductors consists of a constantly rotating multi-contact hunting switch, hereafter referred to as a detector switch, of somewhat unusual design.

More particularly, the detector switch which associates the vacuum tube test means with the marked conductors comprises a large number of stationary terminals, e. g., 25 to 200 terminals, a rotary wiper arranged to wipe over said terminals with a very light contact pressure, and means for maintaining the cooperative, coasting wiping surfaces of the stationary terminals and the moving wipers constantly covered with a film of oil.

It is true that switches operating in oil are known but so far as 1 am aware such switches have always been arranged to operate with comparatively high pressures in order that the film of oil between the coacting contact members may be broken down to provide a satisfactory electrical contact. Furthermore, it is usual to employ, for at least one of the coacting members, a carbon or graphite body or brush since contacts between two metallic members bathed in oil are generally assumed to be unsatisfactory. Moreover, so far as I am aware it has never been proposed to construct a detector type switch (i. e., a constantly rotating hunting switch having a large number of contacts) with lubricating means for flooding or bathing the cooperating contact surfaces'in oil.

In spite of the generally accepted belief that satisfactory contacts for ages below 125 volts) cannot be made between metallic members copiously bathed in oil, at least without the use o very substantial contact pressures, and in spite of the fact that such oil switches as have been manufactured have always been designed with large contact pressures and have been employed for use with high voltages of low voltages (i. e., voltthe order of several hundred volts or more, I have found that very reliable and satisfactory results may be obtained when a constantly rotating detector switch whose contacts are bathed in oil and have low contact pressures, is employed to connect the marked conductors to a sensitive test device responsive to small currents. This is somewhat surprising since it has generally been assumed that an attempt to make contact between members bathed in oil would provide not merely a high resistance connection but rather a substantially open connection so long as the mechanical contact pressure was comparatively low and the applied voltage was insuflicient to cause disruptive breakdown of the oil film. Perhaps the fact is that even with a light contact pressure of the order of 10 grams per. square millimeter or less, the oil film is always ruptured at some point between the cooperative wiping surfaces due to minute roughnesses or irregularity thereof.

In any case whatever the explanation might be, I have found that a detector switch (i, e., a constantly rotating hunting type switch arranged to search successively over 20 or more stationary contacts at a rate of the order of 15-300 contacts per second) may be successfully used to interconnect a thermionic testing mechanism with a marked conductor even when the potential used for marking the conductor is onliy of the order of 48 or 24 volts in magnitude and even when the contact pressures are as low as 20 grams and the contacts are quite smooth, well worn and have an area of about 4 square millimeters.

Preferably, the testing device should be a thermionic apparatus adjusted to respond to very small currents of the order of Sil-8G() microamperesor even less.' and the rate of rotation of the detector switch should be low enough so that this does not wipe over its contacts at a rate of more than 500 contacts per second. With such contact pressures and scanning rates I have found that very reliable operation may be secured even with marking voltages of 24 volts or even 12 volts.

.Accordingly one feature of the present invention is the combination of a detector switch employing low contact pressure and a high contacting rate and having its contact surfaces copiously bathed in oil. with a highly sensitive test device, preferably of thermionic type and adapted to repond to currents of the order of 'l milliampere or ess.

Another feature of the present invention is the provision of a novel switch structure par- Fig. i is a iront elevation of a novel switch in accordance with my invention Fig. 2 is a vertical cross-section substantially along the lines 2 2 'or Fig. l, certain parte being shown in elevation;

Fig. 3 is a schatic circuit diagram of a por= tion of a telephone exchange embodying Referring more particularly to Figs. i and 2, i is a cylindrical casing closed at one end and `molded. of insulating material with a row oi' tels 2 projecting through the side wall. In the structure illustrated, the casing has a diameter of approximately '7 inches and carries 100 terminals. The outside ends of the terminals 22 are accessible for connection and the inside ends protrude far enough from the insulation to be engaged by wipers t and il. Adjacent the terminals 2, feeder strips IE5y and 5 run around the inside wall of cylinder i, with connecting te n.1. 5d and 6a projecting to the outside. Strip 5 extends over apprdiirnately one-half and strip @i over the second half ofcylinder i and they are engaged by the wipers 8a and lla as they wipe over the terminals il.

The open end of the cylindrical casing is closed by a cover l, the closure being made oil-tight by means of a gasket 8. The top l is held in place by screws il.

A housing i@ is fastened to the outside of the cover l. A ball-bearing il is mounted in one side of the housing il) and in alignment therewith a ball-bearing l2 is mounted in the cover l. A shaft i3 with one end seated in bearing it projects through bearing i2 in the cylinder i. An arm M3 is fastened at its midpointgto the shaft i8 within casing i. The wipers 3 and d are supported on the ends of the a id by means oi coiled springs i5, which press the wipers against the inside of the surface oi the cylinder i and thus into engagement with the feeder strips 5 and S and terminals 2 on which they may happen to rest. I have found that ii the surface with which wipers 3 and l cooperate is properly lubricated then the contact pressure may bees low as d@ grams although the wipers perform four complete revolutions per second.

The cylinder i has a cup-shaped extension or well l@ cunlcatingwith the interior of the cylinder. The well i6 is lled with lubricat= ing oil as is' the inside oi the cylinder up to a point indicated by the dotted line il, so that during each revolution the wipers 8 and l can dip into the pool or oil. An oil gauge |18 com municates with the well i6 to indicate the levely of oil in the cylinder. Additional oil may be introduced by removing cap i9 and the oil may be drained' out ci the cylinder by removing screw=cap 2i).

The shaft l] is driven by means or a gear 2&1 mounted thereon intermediate the bearings it, i2. The gear 2i is engaged by a worin 22 mounted on a driving shart 28 inteediate two ball-bearings 263, 2t, which are held in the hous= ing i@ by means oi side plates 2l, 28. The shaft 23 projects through the side plate 2B and may be driven from any suitable source. The chamber 2d, enclosed by the housing is and plates 2li, 2d is nlled with lubricating oil which may be introduced by remo screw d@ and drained 'asseoir out by removing screw 3i. Thus, the driving gear will constantly run in oil.

Referring to Fig. 3 which represents so much or an exchange systemes is necessary for'understg the invention, H, H represent the hoch switches or a number ci' subscribers telephone sets which are respectively connected to the several lines off-b. 'In the central exchange each of these lines o o has connected to it a nber of simple ohmic resistors J, K, L. The L resistor which may be of the order of 5mm!) o is permanently oi each line and its free end is connected to the negative pole of the exchange battery whose positive terminal is grounded in conventional fashion. The K resistor Aassociated with each line is preferably equal in resistance to the L Y resistor and is connected at its free end to a contact of detector switch D preferably through an individual line resistor 3,' the wiper of the detector switch D being connected to the highly sensitive start circuit S over wire lc.

The two wires a, b of each line are further multipled to the terminals or a number of line finders as indicated in the drawings, only two such line nders I and H being shown although it will be lnderstood that ordinarily a larger number will be provided. These line finders are shown as linear motion switches for convenience or illustration, but are preferably single motion rotary switches ofstep by step or power driven type. The a and b wires are also multipled to connector terminals (not shown) in similar fashion.

Within the exchange a third or c wire is also associated with each line as is usual in common battery exchanges and this third or c wire is likewise multipled along with the o. and b Wires to the terminals of the line nders as shown- (and also similarly to the terminals of connectors not shown), each c wire being also connected to the junction between the J and K resistors individual tothe line under consideration.

For starting one or more free line nders to search for a calling line a common start circuit S is provided. This circuit S comprises a vacuum tube V whose anode current constantly energizes an associated relay X except when the grid or this tube V is driven negative by a potential applied to the control wire ic. In the absence oi any current received over control wire 1c the grid of tube V is normally maintained at ground potential, or any other desired reference potential, by high resistance grid leal: G which is connected to ground as shown, or to a bias source of any desired potential. An auxiliary relay Y oi slow release type is provided and connected 'as shown to be operated upon the release of relay X.

ln addition to the coon start circuit S a coon test circuit T generally similar to S is provided. This circuit T comprises the vacuum tube V' whose anode current normally energizes relay X', and also comprises a leak G and an nary relay Y' controlled from relay X'. The grid oi tube ll is connected to the test wire c.

" or the rst free line nder such as line nnder I,

through a common allotting device N which may be a relay chain or selecting switch and which operates in a manner well known per se to connect three wires f, c' and g of the iirst idle line nder'circuit to the corresponding three wires of the v- :u u; test circuit as shown.

The manner of operation or the system shown connected to the b wire l in Fig. 3.is as follows: Upon the raising of the receiver at the calling station (say the station of the second subscribers line I) the hook switch H is closed, thus applying negative potential from the grounded exchange battery over re sistor L, the b wire of the line, hook switch H, the a wire of the line, resistor K, resistor J, start wire k2', to the corresponding contact of the detector switch D. The next time the wiper of this detector switch makes contact with its corresponding contact, this negative potential is extended through the wiper of this switch D, thence over control wire 1c, back contact of relay Y to the grid of tube V in the common start circuit S. The resulting decrease of anode current releases relay X, thus energizing relay Y in an obvious manner. A back contact of relay Y disconnects the grid of V, thus reenergizing relay X, but relay Y remains energized for an interval due to its slow release characteristics. During this energization of relay Y start magnet P of line ilnder I closes an obvious circuit through switch magnet M (in series with its own interrupter contacts if the switch is of step by step type, or directly if it is of power driven type), thus causing wipers W of the line finder switch MW to hunt for the calling line. 1f desired relay P may be omitted from the line iinder of Fig. 3. In such case magnet M and its interrupter if any will be directly connected in place of the relay P. When the wipers W of the line finder switch MW arrive at the calling line, negative potential from the grounded exchange battery is applied to the grid of tube V in common test circuit T (over resistor L, the b wire of the line, hook switch H, the a wire of the line, resistor K, the c wire of the line, corresponding wiper W of the switch MW, the c' wire of the line inder I, the common allotting device N to the grid of tube V'). The resulting reduction of anodel current releases relay X' which causes energization of relay Y in an obvious manner. The operation of relay Y opens the circuit of relay P thus stopping switch magnet M in the line finder. Simultaneously the operation of relay Y energizes relay R in the line iinder which switches through the a and b wires to the two windings of balanced bridge relay Q and simultaneously places ground on the c' wire of the line finder, and on conductor n which extends to the common allotting device thus causing this allotter to disconnect the test circuit T from line iinder I and to prepare to connect this test circuit with the next idle line iinder in known manner. The grounding of the c' wire by relay R in the line iinder effectively removes the negative potential from the grid of tube V since the above traced circuit for ap- Vplying such negative potential to this grid is now by-passed to ground between resistors J and K (over the c wire, corresponding wiper W of switch MW, the c' wire of the line finder I, to the make contact of relay R) As a result relay X' promptly reenergizes but relay Y remains actuated for an interval due to its slow release characteristics. The allotter N should be arranged in known manner so as not to connect test circuit 'I' to the next line finder until after relay Y' has released, although the disconnection of T from line finder I may occur immediately after grounding of wire n as above mentioned.

In the line nder I, which is now connected to the calling line, bridge relay Q energizes over the line loop in the usual fashion, thus holding relay R over an obvious locking circuit'of the latter. The subsequent operations of the equipment beyond the line finder take place in the usual manner preferably under control of bridge relay Q.

It will be noted that now the line is balanced since resistor K is now grounded over the c wire at the end remote from the a side of the line, whereas the equal resistor L which is connected to the b side of the line is connected to the grounded exchange battery, thus providing a balanced line. The resistors K and L are thus effectively in shunt with the windings of bridge relay Q, but since these resistors are many times larger than the impedance of the talking circuit the presence of these resistors introduces substantially no loss in the circuit. It will also be noted that no negative potential is now supplied to the start wire k2' from the calling line above considered, because the intermediate point between the resistors K and J associated with this line is now grounded over the c wire as above A traced. Upon release or" relay Y, therefore, no

negative potential will be applied through the detector switch D to the grid of tube V of the start circuit S until another line initiates a call.

It will also be noted that in case one of the lines shown is called the application of ground .potential to the c Wire of this line from the connector in the usual fashion will similarly serve to balance the line and at the same time to prevent this line from applying negative potential to the common start circuit S when its switch hook His closed to answer the call.

With the type of circuit shown in Fig. 3 the duration of closure of each contact of switch D should be preferably 3 milliseconds or more al though by connecting a condenser around resistor G this time may be somewhat shortened. especially if resistor G is substantially higher than the three resistors J, K and L and the subscribers line in series. Iiesistors J and K may suitably be 5000 to 50,000 ohms apiece, while resistor J may be 11300-2000 ohms or may even be omitted.

The tubes .V and V may be grid controlled gas filled discharge tubes of the trigger type instead of high vacuum tubes so as to remain conducting when once ignited. In such case a special battery with grounded negative may be used for feeding the L resistors and relays X and X may be correspondingly modified to operate upon the initiation or" a cali. Or high vacuum tubes may be used with a self-locking circuit of known type to remain either conducting or nonfconducting until reset. .Any oi these expedients will permit a very brief contacting time for the commutating device D, thus permitting a very rapid operation of this device while still insuring operation (or release) oi relay X.

Although certain embodiments of the invention have been shown and described for purposes of illustration, it will be understood that modifications, adaptations and alterations thereof occurring to one skilled in the art may be made without departing from the scope of the invention as dened in the appended claims.

What I claim is:

l. In a telecommunication exchange system the combination of a hunting switch comprising a number of iixed contacts and a wiper wiping thereacross, means for applying low tension marking potential to one of said xed contacts, means for maintaining the cooperating surfaces of said wiper and contacts continually wet with oil, and test means responsive to weak currents eonneced izo @ne Wine? ci millon iol? ne e to the pieemce ci @nid mining noten nel on cold one of @ein eoniecie.

2. En n teleeccetion excnnnge system c www benk, o, Winer engaging :scid teni benk, mem for continuously moving seid wiper eo cnuee it no wipe repeetedly over eend nenn, menne including eeicl wiper for coni-innowly oiling seid been, menne for apn low tension marking potentiel io e m. z if. ol seid and teal; meens responsive to cursen@ con-f nected to the wiper oi cold switch for nesnon'@ oo the presence of seid marion@ potentiel on mi@ Timm'. al.

3. A telephone inne nun switch ccinp n te :u ir. nl benk, e, einer engaging seid 1'. lo, menne for continuously mog seid meer to conse it to wine repeatedly over ine tenis oi seid benk, and en oil tenth inizowhicli geld Wiper dine periodically during ite momen.

e. In e ielenhone selector centen, n ccsilrie,l n

mw of .elm-- as in seid c, e cover for seid cel., wipers coopereting with said tenis, e :shaft foiiotnting seid wipes, end lnbncn oil'in seid im' inf/o which the Win-en; dip dur each revolution of the elicit. A 5. In n telephone selector switch, e casing of o .1 mnteriel, n row of liercls projecting through the eide w of the ceasing. n cover for said casing, wipers in seid casing x'esiliently pressed against said n eneft for miniing seid wipers proiec H1. rw seid cover, lubricating oil in said in@ ini-o which the wipers dip d f r `if; each relution, n second one ing mounted on said cover, l, M- and n drin gear for i'. wi the second weine. and lubi'icoi; oil ww seid second g.

neeeeii y engagement with seid tels, e. shaft for ro- Eating seid am projecting through seid cover, lubricetine oil in seid cg inn) which the wipers dip during each revolution oi the o. .second casing mounted on seid cove?, bearings and n dri@ geen for geld Sheff'. Within ine second canine, n dri shnfff, having hearings and c 'nom engaging scid geef eiso mounted w: eeid second ce, end lulonoe oil eeid eecond 7. )In e telecouniceon exchange system ine combination ci e constantly operating huntin@ switch comp 11am e, nner of med connecte end n Wiper enping ihereecross with e. preeeure of? le@ enen lo g per square e' @e a mie in excess of l@ contecis per second, ineens for nnpg lon tension rizing nobentiel io one of seid Stationery contente, means for coniinuelly nog seid contacte Wien oil, and elec non charge test means resnonnve lo cimenta oi' leee then one ampere y mi.; to the wiper of seid switch foi' responding Eo the pres ence oi said marking potentiel on seid one ei seid contacts.

8. En e. telephone selector Swich, e ie V 1': including e wiper engem U-r.-.

for moving said wiper over;l the tern of seid bank, and en oil beth into which wiper dine periodically dur its motion. 

